The field of the disclosure relates generally to wireless communication networks, and more particularly, to wireless communication networks utilizing carrier sense multiple access (CSMA).
CSMA with collision avoidance (CSMA/CA) is a network multiple access method, sometimes referred to as “listen-before-talk” (LBT), in which nodes utilize carrier sensing, but attempt to avoid collisions by transmitting only when the channel is sensed to be idle (i.e., not being used). The CSMA/CA protocol typically operates in the data link layer of the telecommunication model of the network. Conventional Wi-Fi, Long Term Evolution (LTE) Licensed Assisted Access (LAA), and MulteFire technologies have recently adopted the CSMA/CA scheme as a mechanism for medium access control (MAC). In such conventional schemes, a transmitter/transceiver of a node defers its transmission (when another node is detected) and applies an additional back off time before starting its own transmission. During this back off time, the node monitors the channel and performs clear channel assessment (CCA). If the channel is not busy at the end of this period, the transmitter/transceiver initiates transmission. The transmitting node then monitors the environment using uniform a beam-pattern, listening for transmissions from all directions.
FIG. 1 is a schematic illustration of a conventional wireless transmission system 100 employing CSMA/CA for a uniform beam pattern 102 radiating from a central transmitter 104. System 100 implements a CSMA/CA protocol in a Wi-Fi/LTE LAA environment. Central transmitter 104 is, for example, a transmitting access point (AP). System 100 includes an intended mobile user 106, which wirelessly receives signals from central transmitter 104 over a communication link 108 under consideration. System 100 further includes a plurality of neighboring APs 110 and a plurality of neighboring mobile users 112, respectively communicating over neighboring links 114.
In this example, the respective APs and mobile users are illustrated as having multiple antennas. In practical operation, a given AP will typically have more antennas and more signal processing capability than a typical mobile user. Operation of neighboring APs 110 and neighboring mobile users 112 generates interferences 116 to and from central transmitter 104. Because beam pattern 102 is uniform in all directions from central transmitter 104, central transmitter backs off equally in the respective focus direction of each interference 116, when detected, and therefore represents an inefficient application of transmission resources.